The secret was revealed at a dinner party attended by actor Michael Sheen who has played the ex-premier in three films.

"Blair's people got progressively more drunk throughout the night and told me more and more inappropriate stories about their boss, who came over to me at the end," The Daily Express quoted Sheen as saying.

"He said, 'They haven't been telling you about...' and then named a few different things that I won't mention before one of his senior staff told him, 'I told him about the Union Jack boxer shorts, Tony.' And he was like, 'Oh no!'" Sheen said.

"It turns out he has a pair of silk Union Jack boxer shorts. I had to put that in the film but the scene got cut out unfortunately. He claims he hasn't seen any of the films where I've played him but I think he's fibbing," he added. (ANI)